Children who consume fermented dairy have higher levels of secretory IgA, LL-37, and α- and β-defensins in their feces compared to those who do not.
Mechanism
Synthesis from 1 study
Good bacteria in fermented dairy stick to the gut and tell immune cells to make more germ-killing proteins like secretory IgA and defensins. These proteins show up in poop at higher levels because they are released directly into the gut to trap and kill harmful microbes.
Most probable mechanism
Good bacteria from fermented dairy stick to the gut lining and trigger immune cells there to make more protective proteins that kill germs and block them from entering the body. These proteins include secretory IgA, LL-37, and defensins, which show up in poop at higher levels after eating fermented dairy.
Probiotic bacteria from fermented dairy survive passage through the stomach and adhere to intestinal epithelial cells and dendritic cells in the gut mucosa.
These bacteria engage pattern recognition receptors (TLR2, NOD2) on immune and epithelial cells, activating intracellular signaling pathways that involve MyD88 and NF-κB.
Signaling through these pathways triggers gene transcription that increases production of antimicrobial peptides (LL-37, α-defensins, β-defensins) and secretory IgA by intestinal epithelial cells and plasma cells in the lamina propria.
These antimicrobial peptides and secretory IgA are secreted into the gut lumen, where they bind to and neutralize pathogens, prevent microbial invasion, and enhance clearance of harmful bacteria.
The secreted antimicrobial peptides and secretory IgA are transported across the epithelial barrier and detected in fecal matter at elevated concentrations.
Less supported by current evidence, but not ruled out
Good bacteria in fermented dairy break down fiber to make short-chain fatty acids, which strengthen the gut lining and stop bacterial toxins from leaking into the blood. This reduces inflammation that could otherwise suppress immune defenses.
Probiotic bacteria ferment dietary fibers to produce short-chain fatty acids (acetate, propionate, butyrate) in the colon.
Short-chain fatty acids bind to receptors on intestinal epithelial cells, increasing expression of tight junction proteins (occludin, claudins) and suppressing zonulin production.
Tightened epithelial barriers reduce translocation of bacterial endotoxins (LPS) from the gut lumen into systemic circulation.
Lower systemic LPS levels reduce activation of TLR4 on macrophages, decreasing production of proinflammatory cytokines (TNF-α, IL-6).
Reduced systemic inflammation preserves mucosal immune function, allowing sustained production of antimicrobial peptides and secretory IgA.
Evidence from Studies
Supporting (1)
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Impact of Fermented Dairy on Gastrointestinal Health and Associated Biomarkers
Contradicting (0)
Community contributions welcome
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